The present invention relates to energy-management systems configured to absorb significant impact energy in a consistent and predictable manner during an impact stroke, including energy absorbers made of polymeric materials.
The federal government, insurance companies, and agencies, associations, and companies concerned with vehicle safety have established standardized impact tests that vehicle bumper systems must pass. Bumper mounts and crush towers are commonly used to support bumper bars on vehicle frames and often are used to absorb energy during a vehicle impact. Several characteristics are beneficial for “successful” bumper mounts and crush towers. It is desirable to manufacture bumper mounts and crush towers that provide consistent and predictable impact strength within a known narrow range, so that it is certain that the bumper systems on individual vehicles will all pass testing. This lets manufacturers make a safer vehicle and also lets them more precisely optimize their bumper systems to reduce excess weight and to utilize lower cost materials. More specifically, it is desirable to manufacture bumper mounts and crush towers that provide a consistent force-vs-deflection curve, and to provide a consistent energy absorption-vs-time curve, and to provide a consistent and predictable pattern of collapse. This lets vehicle manufacturers know with certainty how much deflection is created with any given impacting force, and how much energy is absorbed at any point during an impact or vehicle collision. In turn, this allows vehicle manufacturers to design enough room around the bumper system to permit non-damaging impact without wasting space to compensate for product variation and to provide enough support to the bumper system on the vehicle frame. The force-versus-deflection curve has several important ranges at which the crush tower changes from elastic deformation to permanent deformation to total collapse and bottoming out. It is important that these various points of collapse be predictable to assure that substantial amounts of energy are absorbed before and during collapse, and also to assure that collapse occurs before excessive loads are transferred through the bumper system into the vehicle and its passengers.
In addition to the above, bumper development programs require long lead times, and it is important that any crush tower be flexible, adaptable, and “tunable” so that it can be modified and tuned with predictability to optimize it on a given vehicle model late in a bumper development program. Also, it is desirable to provide a crush tower design that can be used on different bumper beams and with different bumper systems and vehicle models, despite widely varied vehicle requirements, so that each new bumper system, although new, is not a totally untested and “unknown” system.
Some tubular crush towers are known for supporting bumper beams in a bumper system. In one type, two stamped half shells are welded together. However, this process generates raw material scrap. Also, the welding process is a secondary operation that adds to manufacturing overhead costs. Further, the welded crush towers are subject to significant product variation and significant variation in product impact strength, force-versus-deflection curves, energy absorption curves, and crush failure points.
Some crush towers use stronger materials than other crush towers. However, as the strength of a crush tower is increased, there is a tendency to transmit higher and higher loads from the bumper beam directly into the vehicle frame. This is often not desirable. Instead, it is desirable that the tower itself predictably crush and collapse and absorb a maximum of energy over a distributed time period. In particular, crush towers that are very high in strength will tend to transmit undesirably high load spikes from the bumper beam to the vehicle frame. This is often followed by a catastrophic collapse of the crush tower where very little energy is absorbed and where the energy absorption is not consistent or predictable from vehicle to vehicle. Also, it results in premature damage to a vehicle frame. It is particularly important that a crush tower be designed to flex and bend material continuously and predictably over the entire collapsing stroke seen by the crush tower during a vehicle crash. At the same time, a design is desired permitting the use of ultra-high-strength materials, such as high-strength low alloy (HSLA) steels or ultra-high-strength steels which have a very high strength-to-weight ratio. As persons skilled in the art of bumper manufacturing know, the idea of simply making a crush tower out of a stronger material is often a poor idea, and in fact, often it leads to failure of a bumper system due to transmission of high impact loads and load spikes to the vehicle frame, and also to problems associated with insufficient energy absorption.
Vehicle frames, like bumper mounts and crush towers, are preferably designed to manage impact energy, both in terms of energy absorption and energy dissipation. This is necessary to minimize damage to vehicle components, and also is necessary to minimize injury to vehicle passengers. Like bumper mounts and crush towers, vehicle frames have long development times, and further, they often require tuning and adjustment late in their development. Vehicle frames (and frame-mounted components) have many of the same concerns as bumper mounts and crush towers, since it is, of course, the vehicle frame that the mounts and crush towers (and other vehicle components) are attached to.
More broadly, an energy absorption system is desired that is flexible, and able to be used in a wide variety of circumstances and applications. It is preferable that such an energy absorption system be useful both in a bumper system, and also in vehicle frames (longitudinal and cross car), and other applications, as well as in non-vehicle applications. Notably, it is important to control energy absorption even in components made of polymeric materials. For example, injection molded and thermoformed energy absorbers are often used in vehicle bumper systems, such as by placing the polymeric energy absorber on a face of a tubular metal reinforcement beam. It is also important to control initial energy absorption, especially as bumpers are made to improve pedestrian safety during impact by a vehicle.
Accordingly, an energy management system is desired solving the aforementioned problems and having the aforementioned advantages. In particular, an energy management system is desired that provides consistent impact strength, consistent force-vs-deflection curves, consistent energy absorption (for elastic and permanent deformation), and consistent collapse points and patterns, with all of this being provided within tight/narrow ranges of product and property variation. Also, a cost-competitive energy management system is desired that can be made with a reduced need for secondary operations and reduced need for manual labor, yet that is flexible and tunable.